The present invention relates to a wear-resistant member for use in internal combustion engines and a method for producing the same. Such a wear-resistant member is intended for use as a movable member such as for those subjected to high planar pressures such as rocker arms, tappets, camshaft and valve and valve seat.
Recently, there have been requirements for providing lightweight mechanical members thus increasing the efficiency of the engine in which they are employed in accordance with increased requirements for energy-saving and high output in internal combustion engines. Particularly, wear-resistant members are used under severe working conditions so that composite or combination members including different kinds of materials are often used in order to simultaneously provide good wear-resistivity, mechanical strength, and lightness.
According to the conventional techniques for producing such combination member, the technique used for binding together the different materials is of utmost importance. Generally, envelope-molding, brazing and melt-bonding are employed in order to bond a layer of wear-resistant material to a ferrous base member of cast iron or steel. For example U.S. Pat. No. 3,198,182 discloses a tappet produced by melt-bonding and U.S. Pat. No. 2,753,859 discloses a bond method employing infiltration to produce composite sintered material.
In case of bonding a sintered material to a ferrous base member, envelope-molding is employed after sintering. Alternatively, brazing may be conducted after machining the base to predetermined dimension. It is evident that such processes require complicated expensive, and time-consuming manufacturing processes. For envelope-molding, the materials to be used must be specially selected and special techniques are required for its handling. Further, in the case of brazing, excellent bonding strength is not obtainable due to the lack of complete bonding of the material to the base member.
Another technique for bonding has been proposed in Japanese Patent Publication No. 44-6457 in which powders are provided under pressure on the base member and a sinter technique is used. Similarly, in Japanese Patent Publication No. 45-21169, an infiltration material is used. However, these techniques still involve a number of difficulties in their implementation. For example, in case of the second-mention Japanese Patent Publication, the infiltration material, such as copper, does not provide sufficient scuffing resistance.
When a sintered member is applied to a mechanical member subjected to high planar pressure, the porosity of the sintering member should be low in order to adequately withstand the high planar pressure. For this purpose, the sintered may be subjected to coining as described in U.S. Pat. No. 2,673,671. Alternatively, the sintered member may be subjected to hot-compacting. However such techniques still require special skills to manufacture the sintered member. For producing combination members, prior to envelope-molding or brazing, the sintered member must be machined to predetermined dimension to successfully bond the sintered member to the base plate so as to produce combination member.